Valve timing controller

ABSTRACT

A valve timing controller has a case which defines a fluid chamber therein. A magnetic viscosity fluid is enclosed in the fluid chamber. The magnetic viscosity fluid including magnetic particles and its viscosity varies according to a magnetic field applied thereto. A coil and a control circuit applies magnetic field to the magnetic viscosity fluid to variably control a viscosity thereof. A brake rotor is rotatably accommodated in the fluid chamber and receives a brake torque from the magnetic viscosity fluid according to the viscosity thereof. A phase adjusting mechanism is connected to the brake rotor for adjusting a relative rotational phase between the crankshaft and the camshaft according to the brake torque. When it is estimated that the engine will be started, the coil is energized to generated heat in the magnetic viscosity fluid.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No.2010-134431filed on Jun. 11, 2010, the disclosure of which is incorporated hereinby reference.

FIELD OF THE INVENTION

The present invention relates to a valve timing controller which adjustsvalve timing of a valve that is opened/closed by a camshaft driven by atorque transmitted from a crankshaft of an internal combustion engine.

BACKGROUND OF THE INVENTION

Conventionally, it is known that a valve timing controller adjusts arelative rotational phase between a crankshaft and a camshaft accordingto a braking torque generated by an actuator. A valve timing of anintake valve and/or an exhaust valve depends on the above relativerotational phase, which is referred to as an engine-phase.JP-2008-51093A shows such a valve timing controller which adjusts anengine-phase by generating braking torque of a fluid actuator.

Specifically, this valve timing controller has an actuator in whichmagnetic viscosity fluid is enclosed in a casing. The magnetic viscosityfluid is in contact with a braking rotor. A magnetic field is applied tothe magnetic viscosity fluid, whereby a viscosity of the magneticviscosity fluid is variably controlled. The braking torque is generatedon the braking rotor supported by the casing according to the viscosityof the magnetic viscosity fluid. Thus, the engine-phase is adjustedaccording to the braking torque.

Generally, when temperature of the magnetic viscosity fluid extremelyfalls, the magnetic viscosity fluid becomes the glass transitioncondition (solid) in which its viscosity is unstable relative to themagnetic field. Thus, if the magnetic viscosity fluid is brought intothe glass transition condition during an engine stop, it is likely thatnecessary braking torque is not generated at the time the engine isrestarted. In such a case, an optimum engine-phase is not obtained and astartability of the engine is deteriorated. An accuracy of the valvetiming controller is less ensured.

SUMMARY OF THE INVENTION

The present invention is made in view of the above matters, and it is anobject of the present invention to provide a valve timing controller ofwhich reliability is ensured.

According to the present invention, a valve timing controller adjusts avalve timing of a valve opened/closed by a torque transmitted from acrankshaft to a camshaft of an internal combustion engine. The valvetiming controller includes: a case defining a fluid chamber therein; anda magnetic viscosity fluid enclosed in the fluid chamber. The magneticviscosity fluid includes magnetic particles and its viscosity variesaccording to a magnetic field applied thereto.

The valve timing controller further includes: a viscosity control meansfor variably controlling a viscosity of the magnetic viscosity fluid byapplying a magnetic field to the magnetic viscosity fluid; a brake rotorrotatably accommodated in the fluid chamber and receiving a brake torquefrom the magnetic viscosity fluid according to the viscosity thereof; aphase adjusting mechanism connected to the brake rotor for adjusting arelative rotational phase between the crankshaft and the camshaftaccording to the brake torque; and a heating control means forgenerating a heat in the magnetic viscosity fluid when it is estimatedthat the internal combustion engine will be started.

When it is estimated that the engine will be started, the coil isenergized to generate heat in the magnetic viscosity fluid. Even if themagnetic viscosity fluid is in the glass transition condition, themagnetic viscosity fluid is brought out from the glass transitioncondition, whereby the variation in viscosity becomes stable accordingto the applied magnetic field. Consequently, when the engine is started,the viscosity of the magnetic viscosity fluid can be controlled byapplying the magnetic field thereto, whereby desired brake torque isinputted into the brake rotor so that the phase adjusting mechanismmakes the engine-phase optimal. Therefore, a high reliability of thevalve timing controller can be ensured.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome more apparent from the following description made with referenceto the accompanying drawings, in which like parts are designated by likereference numbers and in which:

FIG. 1 is a cross sectional view showing a valve timing controlleraccording to a first embodiment of the present invention, taken along aline in FIG. 2;

FIG. 2 is a cross-sectional view taken along a line II-II in FIG. 1;

FIG. 3 is a cross-sectional view taken along a line in FIG. 1;

FIG. 4 is a characteristics chart for explaining a magnetic viscosityfluid;

FIG. 5 is another characteristics chart for explaining a magneticviscosity fluid;

FIG. 6A and FIG. 6B are time charts for explaining an energizationcontrol according to the first embodiment;

FIG. 7 is a characteristics chart for explaining a heating of themagnetic viscosity fluid according to the first embodiment;

FIG. 8 is a flowchart showing a control flow of an energization controlcircuit according to the first embodiment;

FIG. 9A and FIG. 9B are time charts for explaining an energizationcontrol according to a second embodiment;

FIG. 10A and FIG. 10B are time charts for explaining an energizationcontrol according to a third embodiment;

FIG. 11 is a flowchart showing a control flow of an energization controlcircuit according to a fourth embodiment;

FIG. 12 is a flowchart showing a control flow of an energization controlcircuit according to a fifth embodiment;

FIG. 13 is a cross sectional view showing a valve timing controlleraccording to a sixth embodiment;

FIG. 14 is a flowchart showing a control flow of an energization controlcircuit according to a sixth embodiment; and

FIG. 15 is a flowchart showing a control flow of an energization controlcircuit according to a seventh embodiment;

DETAILED DESCRIPTION OF EMBODIMENTS

Multiple embodiments of the present invention will be described withreference to accompanying drawings. In each embodiment, the same partsand the components are indicated with the same reference numeral and thesame description will not be reiterated. Further, each embodiment can besuitably combined.

First Embodiment

FIG. 1 shows a valve timing controller 1 according to a first embodimentof the present invention. The valve timing controller 1 is mounted on avehicle, and more specifically, the valve timing controller 1 is mountedon a transmission system that transmits an engine torque from acrankshaft (not shown) to a camshaft 2 of an internal combustion engine.In the present embodiment, the camshaft 2 opens and closes an intakevalve (not shown) of the internal combustion engine through transmissionof the engine torque. The valve timing controller 1 adjusts a valvetiming of the intake valve.

As shown in FIGS. 1 to 3, the valve timing controller 1 includes anactuator 100, a current control circuit 200, a phase adjusting mechanism300 and the like. The valve timing controller 1 adjusts a relativerotational phase between the crankshaft and the camshaft 2 to realize adesired valve timing.

(Actuator 100)

As shown in FIG. 1, the actuator 100 is an electromotive fluid brakewhich is comprised of a case 110, a brake rotor 130 and a coil 150.

The case 110 is comprised of a fixed member 111 and a cover member 112.The fixed member 111 is annular-shaped and is made of magnetic material.The fixed member is fixed on a chain case (not shown) of the internalcombustion engine. The cover member 112 is also made of magneticmaterial. The cover member 112 and the fixed member 111 define a fluidchamber 114 therebetween.

The brake rotor 130 is made of magnetic material and includes a shaftportion 131 and a rotor portion 132. The shaft portion 131 extendsthrough the fixed member 111 to be connected with the phase adjustingmechanism 300. The other end of the shaft portion 131 is rotatablysupported by the cover member 112 through a bearing 115. A middleportion of the shaft portion 131 is supported by the fixed member 111through a bearing 116. When receiving an engine torque from the phaseadjusting mechanism 300, the brake rotor 130 rotates counterclockwise inFIGS. 2 and 3.

The rotor portion 132 is disc-shaped and is accommodated in the fluidchamber 114. A first magnetic gap 114 a is defined between the rotorportion 132 and the fixed member 111. A second magnetic gap 114 b isdefined between the rotor portion 132 and the cover member 112.

The magnetic viscosity fluid 140 is enclosed in the fluid chamber 114.The magnetic viscosity fluid 140 is functional fluid comprised ofbase-liquid and magnetic particles. The base-liquid is nonmagnetic fluidsuch as oil. Preferably, the base-liquid is lubrication oil for anengine. The magnetic particles are magnetic powder of carbonyl iron.

As shown in FIG. 4, the magnetic viscosity fluid 140 has characteristicsin which its viscosity increases according to an intensity of appliedmagnetic field. Further, in proportion to the viscosity, its shear yieldstress also increases. Further, in a condition where no magnetic fieldis applied to the magnetic viscosity fluid 140, the base viscosity ofthe magnetic viscosity fluid 140 is increased along with a decrease intemperature thereof. When the temperature is excessively decreased, themagnetic viscosity fluid 140 becomes the glass transition condition(solid) in which its viscosity is unstable relative to the magneticfield. In the present embodiment, a lower limit temperature “Tl” of themagnetic viscosity fluid 140 is set at “−20° C.”.

A coil 150 is winded around a resin bobbin coaxially to the fixed member111. When the coil 150 is energized, magnetic field is generated in sucha manner that magnetic flux passes through the first magnetic gap 114 a,the rotor portion 132, the second magnetic gap 114 b, the cover member112 and the fixed member 111. The generated magnetic field is applied tothe magnetic viscosity fluid 140 in the magnetic gaps 114 a, 114 b, sothat its viscosity is varied. Thus, between the case 110 and the brakerotor 130, braking torque is generated to brake the brake rotor 130 inclockwise direction in FIGS. 2 and 3. As above, when the coil 150 isenergized to generate the magnetic field which is applied to themagnetic viscosity fluid 140, the braking torque is inputted into thebrake rotor 130 according to the viscosity of the magnetic viscosityfluid 140.

As shown in FIG. 1, the resin bobbin 151 is exposed to the firstmagnetic gap 114 a in the fluid chamber 114. The fixed member 111 isalso exposed to the first magnetic gap 114 a. Thus, even if the coil 150generates heat when energized, the heat is transferred to the magneticviscosity fluid 140 in the first magnetic gap 114 a through the resinbobbin 151 and the fixed member 111.

(Current Control Circuit 200)

The current control circuit 200 includes a microcomputer and iselectrically connected to the coil 150 and a battery 4 of a vehicle.When a specified starting condition “Cw” is established with the enginestopped, the current control circuit 200 receives electricity from thebattery 4, whereby the current control circuit 200 is changed fromOFF-mode to ON-mode so that the coil 150 can be energized. The startingcondition “Cw” is established when a door lock of a vehicle is released,a vehicle door is opened, or a receiver receives a signal from atransmitter of a keyless entry system. If the engine is not started evenafter a specified time “ST” elapses from changing mode to the ON-mode,the ON-mode is automatically changed to the OFF-mode.

During the On-mode, the current control circuit 200 controls electriccurrent “I” supplied to the coil 150 so that the magnetic field appliedto the magnetic viscosity fluid 140 is adjusted. Consequently, accordingto the applied magnetic field, the viscosity of the magnetic viscosityfluid 140 is variably controlled so that the braking torque to the brakerotor 130 is increased/decreased.

In the present embodiment, the electric current “I” is controlled asshown in FIG. 6A, so that the magnetic flux density “B” applied to themagnetic viscosity fluid 140 is varied before and after the engine isstarted as shown in FIG. 6B. Specifically, during a period “α” in whichthe engine is not started, the electric current “I” is controlled insuch a manner that the electric current “I” is varied like pulses havinglow frequency “fα” and an effective electric power in a specified period“RT” is high effective electric power “Wα” around 5 W·s. During a period“β” in which the engine is started, the electric current “I” iscontrolled in such a manner that the electric current “I” is varied likepulses having high frequency “fβ” and an effective electric power in aspecified period “RT” is low electric power “Wβ”.

According to the above energization control, during the period “α”, themagnetic particles in the magnetic viscosity fluid 140 repeatedlyperform a movement in which chain-shaped cluster of the magneticparticles is composed and decomposed according to a variation inmagnetic flux density “B” as shown in FIG. 6B. As the result, themagnetic viscosity fluid 140 generates heat due to the above movement ofthe magnetic particles. As shown in FIG. 7, in a case that the appliedelectric current has low frequency “fα”, such as 2-10 Hz, the magneticviscosity fluid 140 effectively generates heat. Further, the magneticviscosity fluid 140 receives heat from the coil 150, so that thetemperature of the magnetic viscosity fluid 140 is effectivelyincreased.

During the period “β”, the electric current “I” has high frequency “fβ”around 50 Hz to generate low electric power “Wβ” around 3 W·s. Further,as shown in FIG. 6B, the magnetic flux density “B” is varied accordingto the frequency “fβ”, the magnetic viscosity fluid 140 receives anagitation action. Thus, the variation in viscosity of the fluid 140becomes stable with respect to the applied magnetic field, and thedesired braking torque can be obtained stably.

It should be noted that the current control circuit 200 controls theenergization of other electrical components.

(Phase Adjusting Mechanism 300)

As shown in FIGS. 1 to 3, the phase adjusting mechanism 300 is providedwith a driving rotor 10, a driven rotor 20, an assist member 30, aplanetary carrier 40 and a planetary gear 50.

The driving rotor 10 is comprised of a gear member 12 and a sprocketmember 13, which are coaxially connected with each other by a bolt. Thegear member 12 includes a first internal gear 14 on its radially innerperipheral wall. The first internal gear 14 defines an addendum circlelocated radially inside of a root circle. As shown in FIG. 1, thesprocket member 13 has a plurality of gear tooth 16 on its outerperiphery. A timing chain (not shown) is wound around the gear teeth 16of the sprocket member 13 and a plurality of gear teeth of thecrankshaft so that the sprocket member 13 is linked to the crankshaft.When the engine torque is transmitted from the crankshaft to thesprocket member 13 through the timing chain, the driving rotor 10rotates in accordance with the crankshaft. A rotation direction of thedriving rotor 10 is a counterclockwise direction in FIGS. 2 and 3.

As shown in FIGS. 1 and 3, the driven rotor 20 is coaxially arranged inthe sprocket member 13. The driven rotor 20 has a connection portion 21on a bottom wall portion thereof. The connection portion 21 is coaxiallycoupled with the camshaft 2. This coupling enables the driven rotor 20to rotate synchronously with the camshaft 2 and to rotate relativelywith respect to the driving rotor 10. The rotational direction of thedriven rotor 20 corresponds to the counterclockwise direction in FIGS. 2and 3.

As shown in FIG. 1, the driven rotor 20 includes a second internal gear22 on its radially inner peripheral wall. The second internal gear 22defines an addendum circle located radially inside of a root circle. Thesecond internal gear 22 has an inner diameter larger than an innerdiameter of the first internal gear 14, and the number of teeth of thesecond internal gear 22 is greater than the number of teeth of the firstinternal gear 14. The second internal gear 22 is positioned away fromthe first internal gear 14 in its axial direction.

The assist member 30 is a torsion coil springs and is coaxially arrangedinside of the sprocket member 13. One end 31 of the assist member 30 isengaged with the sprocket member 13, and the other end 32 is engagedwith the connection portion 21. The assist member 30 generates assisttorque between the driving rotor 10 and the driven rotor 20 so that thedriven rotor 20 is biased in a retard direction relative to the drivingrotor 10.

The cylindrical planetary carrier 40 has a torque-receiving portion 41to which the braking torque is transmitted from the brake rotor 130. Thetorque-receiving portion 41 which is coaxial to the shaft portion 131includes a pair of grooves 42 with which a joint 43 is engaged. Throughthe joint 43, the torque-receiving portion 41 is connected to the shaftportion 131. The planetary carrier 40 rotates along with the brake rotor130 and performs a relative rotation with respect to the driving rotor10. It should be noted that the planetary carrier 40 and the brake rotor130 rotate in counterclockwise direction in FIGS. 2 and 3.

As shown in FIGS. 1 to 3, the planetary carrier 40 has a supportingportion 46 which supports the planetary gear 50. The supporting portion46 is arranged eccentrically with respect to the shaft portion 131 andis coaxially engaged with a center hole 51 of the planetary gear 50through a planetary bearing 48. The planetary gear 50 is supported bythe supporting portion 46 in such a manner as to perform the planetarymotion. The planetary gear 50 rotates about an eccentric axis of thesupporting portion 46, and also the planetary gear 50 revolves relativeto the planetary carrier 40. Thus, when the planetary carrier 40performs relative rotation with respect to the driving rotor 10 in therevolution direction of the planetary gear 50, the planetary gear 50performs the planetary motion.

The planetary gear 50 has a first external gear 52 and a second externalgear 54. The first external gear 52 engages with the first internal gear14. The second external gear 54 engages with the second internal gear22. The second external gear 54 has an outer diameter larger than thatof the first external gear 52. The number of gear teeth of the secondexternal gear 54 and the first external gear 52 is smaller than thenumber of teeth of the internal gears 22, 14 by the same number of gearteeth.

The above phase adjusting mechanism 300 adjusts the engine-phaseaccording to a balance between the braking torque of the brake rotor130, the assist torque of the assist member 30 and the variable torquetransmitted from the camshaft 2 to the brake rotor 130.

Specifically, when the brake rotor 130 rotates at the same speed as thedriving rotor 10, the planetary carrier 40 does not perform a relativerotation with respect to the driving rotor 10. Thus, the planetary gear50 rotates along with the rotors 10, 20 without performing the planetarymotion, so that the engine-phase is maintained.

Meanwhile, when the brake rotor 130 rotates at a lower speed than thedriving rotor 10 against the assist torque, the planetary carrier 40rotates in a retard direction relative to the driving rotor 10. As theresult, the planetary gear 50 performs the planetary motion and thedriven rotor 20 relatively rotates in the advance direction with respectto the driving rotor 10, so that the engine-phase is advanced.

Meanwhile, when the brake rotor 130 rotates at faster speed than thedriving rotor 10, the planetary carrier 40 rotates in the advancedirection relative to the driving rotor 10. As the result, the planetarygear 50 performs the planetary motion and the driven gear 20 rotates inthe retard direction relative to the driving rotor 10, so that theengine-phase is retarded.

(Control Flow)

Referring to FIG. 8, a control flow which the current control circuit200 executes will be described hereinafter.

In step S100, the computer determines whether a pre-starting condition“Cs” is established with respect to the engine which is stopped. Thepre-starting condition “Cs” includes any event which occurs prior to astarting of the engine.

When the answer is YES in step S100, the procedure proceeds to step S101in which the computer determines whether an interior of the case 110 isin a low-temperature condition “Sl” in which the temperature of themagnetic viscosity fluid 140 is lower than the lower limit temperature“Tl”.

When the answer is YES in step S101, the procedure proceeds to step S102in which the coil 150 is energized for the period “α”. Consequently, thecoil 150 receives electricity of low frequency “fα”, which generates thehigh electric power “Wα”. The effective heating of the magneticviscosity fluid 140 is started.

In step S103, the computer determines whether an engine start command“Os”, such as turning on of an ignition switch, is detected. When theanswer is YES in step S103, the procedure proceeds to step S104 in whicha cranking of the engine is started and the coil is deenergized. Thus,until the engine is started, the magnetic viscosity fluid 140 has beeneffectively heated.

In step S105, the coil 150 is started to be energized for the period“β”. Consequently, the coil 150 receives electricity of high frequency“fβ”, which generates the low electric power “Wβ”. In a condition wherethe magnetic viscosity fluid 140 is agitated and is less heated, thebraking torque is generated to adjust the engine-phase.

In step S106, the computer determines whether a complete combustioncondition “Ss” of the engine is detected. When the answer is YES in stepS106, the present control flow is terminated. Thus, when the engine isstarted, the magnetic viscosity fluid 140 stably generates the brakingtorque, so that the stable engine-phase adjustment is achieved.

When the answer is NO in step S101, the procedure proceeds to step S107in which the computer determines whether the engine start command “Os”is detected. When the answer is YES is step S107, the procedure proceedsto steps S105 and 8106 in which the coil 150 is energized for the period“β”.

According to the above embodiment, even if the magnetic viscosity fluid140 is in the low-temperature condition “Sl”, the magnetic viscosityfluid 140 is surely heated when it is estimated that the engine will bestarted. As the result, the viscosity of the magnetic viscosity fluid140 depends on the applied magnetic field. When the engine is started,the viscosity of the magnetic viscosity fluid 140 less depends on itstemperature, so that desired braking torque can be stably inputted intothe brake rotor 130. Therefore, since the phase adjusting mechanism 300connected to the brake rotor 130 optimizes the engine-phase for startingthe engine, high reliability of the valve timing controller 1 can beensured.

In the above first embodiment, the coil 150 and the current controlcircuit 200 correspond to a viscosity control means of the presentinvention. Also, the coil 150 and the current circuit 200 correspond toa heating control means of the present invention.

Second Embodiment

As shown in FIGS. 9A and 9B, the second embodiment is a modification ofthe first embodiment. In an energization control step during the period“α”, which corresponds to step S102 in FIG. 8, alternate electriccurrent having low frequency “fα” is applied to the coil 150 as shown inFIG. 9A. The effective electric power in a specified period “RT” is higheffective electric power “Wα”. As the result, as shown in FIG. 9B, themagnetic flux density “B” which varies at low frequency “fα” is appliedto the magnetic viscosity fluid 140. The magnetic viscosity fluid 140generates heat due to the movement of the magnetic particles andreceives heat from the coil 150 which generates heat according to thehigh electric power “Wα”.

During the period “β”, alternate electric current having high frequency“fβ” is applied to the coil 150. The effective electric power in aspecified period “RT” is low effective electric power “Wβ”. As theresult, the magnetic viscosity fluid less generates heat during theperiod “β”.

Thus, also in the second embodiment, even if the magnetic viscosityfluid 140 is in the low-temperature condition “Sl”, the magneticviscosity fluid 140 is surely heated when it is estimated that theengine will be started. When the engine is started, the viscosity of themagnetic viscosity fluid 140 depends on the applied magnetic field. Thevariation in viscosity becomes stable. Thus, the desired braking torquecan be stably inputted into the brake rotor 130. The engine phase whichthe phase adjusting mechanism 300 adjusts is optimized. A highreliability of the valve timing controller 1 can be ensured.

Third Embodiment

As shown in FIG. 10, a third embodiment is a modification of the firstembodiment, During the period “α”, a constant electric current “Iα” isapplied to the coil 150, The effective electric power in a specifiedperiod “RT” is high effective electric power “Wα”. As the result, asshown in FIG. 10B, the magnetic flux density “B” which is constant isapplied to the magnetic viscosity fluid 140. The magnetic viscosityfluid 140 generates heat due to the movement of the magnetic particlesand receives heat from the coil 150 which generates heat according tothe high electric power “Wα”.

During the period “β”, a constant electric current “Iβ” is applied tothe coil 150. The effective electric power in a specified period “RT” islow effective electric power “Wβ”. Thus, the magnetic viscosity fluid140 less generates heat during the period “β”.

Thus, also in the third embodiment, even if the magnetic viscosity fluid140 is in the low-temperature condition “Sl”, the magnetic viscosityfluid 140 is surely heated when it is estimated that the engine will bestarted. When the engine is started, the viscosity of the magneticviscosity fluid 140 depends on the applied magnetic field. The variationin viscosity becomes stable. Thus, the desired braking torque can bestably inputted into the brake rotor 130. The engine-phase which thephase adjusting mechanism 300 adjusts is optimized. A high reliabilityof the valve timing controller 1 can be ensured.

Fourth Embodiment

As shown in FIG. 11, a fourth embodiment is a modification of the firstembodiment. In a control flow of the fourth embodiment, step S400 andstep S401 are included.

Specifically, in step S400, the computer determines whether atemperature of the magnetic viscosity fluid is in a normal-temperaturecondition “Sn” in which the temperature of the magnetic viscosity fluid140 is greater than the lower limit temperature “Tl”.

Until the normal-temperature condition “Sn” is detected, the processesin steps S103 and S400 are repeatedly performed, so that the magneticviscosity fluid 140 effectively generates heat. Meanwhile, when theanswer is YES in step S400, the procedure proceeds to step S401 in whichthe energization in the period “α” is terminated with the enginestopped. Then, the procedure proceeds to step S107 in which the computerdetermines whether the engine start command “Os” is generated. It shouldbe noted that the specified time “ST” of the current control circuit 200is suitably varied to avoid a situation where the temperature of themagnetic viscosity fluid 140 becomes lower than the lower-limittemperature “Tl”.

According to the fourth embodiment, from the time when it is estimatedthat the engine will be started until the time when the temperature ofthe magnetic viscosity fluid exceeds “Tl”, the magnetic viscosity fluidgenerates heat therein. Thus, when the engine is started, the viscosityof the magnetic viscosity fluid depends on the applied magnetic field.

Fifth Embodiment

As shown in FIG. 12, a fifth embodiment is a modification of the fourthembodiment. In a control flow of the fifth embodiment, step S500 isincluded instead of step S400.

Specifically, in step S500, the computer determines whether a specifiedheat-generating period “HT” has elapsed. It should be noted that thespecified heat-generating period “HT” is required for the magneticviscosity fluid 140 to be brought in the normal-temperature condition“Sn”. The heat-generating period “HT” is previously determined based onthe low-frequency “fα” and the high effective electric power “Wα”.

Until the heat-generating period “HT” has elapsed, the processes insteps S103 and S500 are repeatedly performed, so that the magneticviscosity fluid 140 effectively generates heat. Meanwhile, when theanswer is YES in step S500, the procedure proceeds to step S401 in whichthe energization in the period “α” is terminated with the enginestopped. Then, the procedure proceeds to step S107 in which the computerdetermines whether the engine start command “Os” is generated.

According to the fifth embodiment, from the time when it is estimatedthat the engine will be started until the heat-generating period “HT”has passed, the magnetic viscosity fluid generates heat therein. Thus,when the engine is started, the viscosity of the magnetic viscosityfluid depends on the applied magnetic field.

Sixth Embodiment

As shown in FIG. 13, a sixth embodiment is a modification of the firstembodiment. An actuator 600 includes the coil 150 and a second coil 650for generating heat in the magnetic viscosity fluid 140.

Specifically, the second coil 150 is winded around a resin bobbin 651coaxially to the cover member 112. When the second coil 650 isenergized, magnetic field is generated in such a manner that magneticflux passes through the cover member 112, the second magnetic gap 114 b,the rotor portion 132, the first magnetic gap 114 a and the fixed member111. The generated magnetic field is applied to the magnetic viscosityfluid 140 in the magnetic gaps 114 a, 114 b.

The cover member 112 is exposed to the second magnetic gap 114 b. Thus,if the second coil 650 generates heat when energized, the heat istransferred to the magnetic viscosity fluid 140 in the second magneticgap 114 b through the resin bobbin 651 and the cover member 112. In thepresent embodiment, the cover member 112 is comprised of two bodies 612a, 612 b made from magnetic material.

The coil 150 and the second coil 650 are electrically connected to acurrent control circuit 620. The current control circuit 620 has thesame configuration and function as the current control circuit 200 inthe first embodiment. Further, the current control circuit 620 cancontrol the energization of the second coil 650 independently from thecoil 150.

In a control flow of the sixth embodiment, step S600 is included insteadof step S102, as shown in FIG. 14. In step S600, the second coil 650 isenergized during the period “α”. Consequently, the second coil 650receives electricity of low frequency “fα”, which generates the highelectric power “Wα”. The effective heating of the magnetic viscosityfluid 140 is started in a similar way of the first embodiment. Until theengine start command “Os” is generated, the magnetic viscosity fluid 140effectively generates the heat therein.

Thus, also in the sixth embodiment, even if the magnetic viscosity fluid140 is the glass transition condition, the second coil 650 is energizedwhen it is estimated that the engine will be started, so that themagnetic viscosity fluid 140 surely generates heat therein. When theengine is started, the second coil 650 is surely deenergized. Thus, instep S105, the magnetic viscosity fluid 140 less receives thermalinfluence. As above, the heat-generation control and the viscositycontrol of the magnetic viscosity fluid 140 can be suitably executed.

In the above sixth embodiment, the coil 150 and the current controlcircuit 620 correspond to a viscosity control means of the presentinvention. Also, the second coil 650 and the current control circuit 620correspond to a heating control means of the present invention.

Seventh Embodiment

As shown in FIG. 15, a seventh embodiment is a modification of the sixthembodiment. In a control flow of the seventh embodiment, step S700 tostep S703 are included.

Specifically, in step S700, the cranking of the engine is started andthe energization control of during the period “α” is continued even inthe period “β”. Then, the procedure proceeds to step S105.

In step S701, the computer determines whether the engine-phase ischanged after performing step S105. A variation in the engine-phase iscomputed based on output signals from a crank angle sensor (not shown)and a camshaft sensor (not shown). When this variation exceeds thespecified quantity “Δθ”, the computer determines that the engine-phaseis changed. When the variation in the engine-phase is detected in stepS701, the procedure proceeds to step S702 in which the second coil 650is deenergized. Then, the procedure proceeds to step S106. Thus, untilthe engine-phase is varied, the magnetic viscosity fluid 140 effectivelygenerates heat therein.

When the engine start command “Os” is detected in step S107, theprocedure proceeds to step S703 and step 106. The coil 150 is energizedduring the period “β”.

According to the seventh embodiment, from the time when it is estimatedthat the engine will be started until the engine-phase is completelychanged, the magnetic viscosity fluid generates heat therein. Thus, whenthe engine is started, the viscosity of the magnetic viscosity fluiddepends on the applied magnetic field.

Other Embodiment

The present invention should not be limited to the disclosureembodiment, but may be implemented in other ways without departing fromthe sprit of the invention.

Specifically, in the first, second, forth to seventh embodiments, duringthe period “β”, the effective electric power may be set greater than orequal to the electric power “Wα” while the frequency is changed from“fα” to “fβ”. Also, in the third embodiment, during the period “β”, theeffective electric power may be set greater than or equal to theelectric power “Wα”.

In the first, second and fourth to seventh embodiments, during theperiod “α” and the period “β”, the frequency “fα”, “fβ” may be varieddirectly or indirectly. In the first second and fourth to seventhembodiments, during the period “α” and the period “β”, the frequency ofthe electric current “I” can be set smaller than or equal to thefrequency “fα” while the effective electric power is changed from “Wα”to “Wβ”. In the sixth and seventh embodiments, it may be configured thatthe magnetic field generated by the second coil 650 is less applied tothe magnetic viscosity fluid. In such a case, the frequency of theelectric current “I” supplied to the second coil 650 is not necessary tobe controlled.

In the control flow of the second, third, sixth, and seventhembodiments, between step S102 and S103 or between step S600 and S103,the processes of steps S400 and S401 in the fourth embodiment may beadded. When the normal-temperature condition “Sn” is detected in stepS400, the procedure proceeds to step S401 and then proceeds to stepS107. Also, in the control flow of the second, third, sixth, and seventhembodiments, between step S102 and S103 or between step S600 and S103,the processes of steps S500 and S401 in the fifth (fourth) embodimentmay be added. When it is determined that the heating period “HT” haselapsed in step S500, the procedure proceeds to step S401 and thenproceeds to step S107. Furthermore, in the control flow of the sixth andseventh embodiments, the energization control in step S102 of the secondembodiment or the third embodiment can be executed in step S600 withrespect to the coil 650.

The configuration of the phase adjusting mechanism 300 is suitablyvariable.

In the first to seventh embodiments, the directions of “advance” and“retard” can be changed therebetween. The present invention isapplicable also to a controller which adjusts the valve timing of theexhaust valve, and a controller which adjusts the valve timings of theintake valve and the exhaust valve.

1. A valve timing controller which adjusts a valve timing of a valveopened/closed by a torque transmitted from a crankshaft to a camshaft ofan internal combustion engine, the valve timing controller comprising: acase defining a fluid chamber therein; a magnetic viscosity fluidenclosed in the fluid chamber, the magnetic viscosity fluid includingmagnetic particles, the magnetic viscosity fluid having a viscositywhich varies according to a magnetic field applied thereto; a viscositycontrol means for variably controlling a viscosity of the magneticviscosity fluid by applying a magnetic field to the magnetic viscosityfluid; a brake rotor rotatably accommodated in the fluid chamber andreceiving a brake torque from the magnetic viscosity fluid according tothe viscosity thereof; a phase adjusting mechanism connected to thebrake rotor for adjusting a relative rotational phase between thecrankshaft and the camshaft of the internal combustion engine accordingto the brake torque which is inputted into the brake rotor; and aheating control means for generating a heat in the magnetic viscosityfluid when it is estimated that the internal combustion engine will bestarted.
 2. A valve timing controller according to claim 1, wherein theheating control means starts a heating of the magnetic viscosity fluidto generate heat therein when it is estimated that the internalcombustion engine will be started and it is detected that a temperatureof the magnetic viscosity fluid is lower than a lower-limit temperaturewhich is required to vary the relative rotational phase.
 3. A valvetiming controller according to claim 1, wherein the heating controlmeans includes a coil disposed in the case, and when the coil isenergized, a magnetic field of which intensity is variable is applied tothe magnetic viscosity fluid, whereby the magnetic viscosity fluidgenerates the heat therein.
 4. A valve timing controller according toclaim 1, wherein the heating control means includes a coil disposed inthe case, and when the coil is energized, the coil generates heat whichis transmitted to the magnetic viscosity fluid, whereby the magneticviscosity fluid is heated.
 5. A valve timing controller according toclaim 3, wherein the heating control means energizes the coil togenerate a magnetic field which is applied to the magnetic viscosityfluid, whereby the viscosity of the magnetic viscosity fluid is variablycontrolled.
 6. A valve timing controller according to claim 5, whereinthe heating control means sets a first variable frequency of themagnetic field when it is estimated that the engine will be started, andthe heating control means sets a second variable frequency of themagnetic field which is higher than the first variable frequency whenthe engine is started.
 7. A valve timing controller according to claim5, wherein the heating control means sets a first electric powersupplied to the coil when it is estimated that the engine will bestarted, and the heating control means sets a second electric powersupplied to the coil, which is lower than the first electric power, whenthe engine is started.
 8. A valve timing controller according to claim3, wherein the heating control means further includes a second coil, andthe viscosity control means energizes the second coil to generate amagnetic field which is applied to the magnetic viscosity fluid, wherebythe viscosity of the magnetic viscosity fluid is variably controlled. 9.A valve timing controller according to claim 8, wherein the viscositycontrol means controls the viscosity of the magnetic viscosity fluid inorder to vary the relative rotational phase when the engine is started,and the heating control means terminates heating of the magneticviscosity fluid when a variation in the relative rotational phase isdetected.
 10. A valve timing controller according to claim 1, whereinthe heating control means terminates heating of the magnetic viscosityfluid when it is detected that a temperature of the magnetic viscosityfluid exceeds a lower-limit temperature which is required to vary therelative rotational phase.
 11. A valve timing controller according toclaim 1, wherein the heating control means terminates heating of themagnetic viscosity fluid when a specified heating period has elapsed,which is required to increase the temperature of the magnetic viscosityfluid higher than a lower-limit temperature which is required to varythe relative rotational phase.
 12. A valve timing controller accordingto claim 1, wherein the heating control means terminates heating of themagnetic viscosity fluid when the internal combustion engine is started.